1. Field of the invention
The present invention generally relates to an optical semiconductor device provided by utilizing an optical semiconductor chip such as an LED chip.
2. Description of the Related Art
A light emitting diode (LED) has advantages such as small power consumption, small size and long lifetime. Therefore, an optical semiconductor device incorporating an LED chip can be advantageously used as a light source for the display of a cellular phone or a notebook computer, for example. Such an optical semiconductor device is so designed as to enhance the brightness. For example, JP-A-2000-183407 discloses the provision of an optical reflector surrounding the LED chip.
FIG. 8 shows an optical semiconductor device as a related art of the present invention. The illustrated semiconductor device B includes a substrate 101, an LED chip 102 mounted on the substrate, and a light permeable member 103 covering the LED chip. The light permeable member 103 has a flat upper surface (light emitting surface) 131 for emitting light. The light permeable member 103 is surrounded by a reflector 104. The reflector 104 has an inclined surface (light reflecting surface) 141 adjoining the light permeable member 103.
As shown in FIG. 8, the light L11 traveling straight up from the LED chip 102 is emitted to the outside through the light emitting surface 131. The light L14 traveling horizontally from the LED chip 102 is reflected upward by the light reflecting surface 141 of the reflector 104. Thus, the amount of light emitted from the light emitting surface 131 of the light permeable member can be increased by reflecting the light traveling horizontally from the LED chip 102 upward.
However, the semiconductor device B still has a room for improvement for enhancing the brightness, because the semiconductor device B has the following problems.
The light coming out from the LED chip 102 impinges on the light emitting surface 131 at various incidence angles. The incidence angles can be divided into those which are larger than the total reflection critical angle and those which are smaller than the total reflection critical angle. For example, the incidence angle α12 of the light L12 shown in FIG. 8 is smaller than the total reflection critical angle αc. The incidence angle α13 of the light L13 shown in FIG. 8 is larger than the total reflection critical angle αc. Therefore, the light L13 is totally reflected by the light emitting surface 131 and cannot be emitted to the outside of the light permeable member 103.
As noted above, in the optical semiconductor device B, some of the light coming out from the LED chip 102 may not be emitted to the outside from the light emitting surface 131. Such light is attenuated while undergoing repetitive reflection within the optical semiconductor device B and cannot be utilized as light for illumination.